Apparatus for fitting spectacles serve to precisely determine the optical centering for spectacle frames already fitted anatomically. The vertical distance of the center point from the zero viewthrough point is dependent, inter alia, upon the inclination of the frame. The zero viewthrough point is that point in the plane of the frame through which the fixation line of the eye passes at the zero view direction. This vertical distance is necessary for the satisfaction of the rotation point requirement of the eye. Accordingly, spectacles fitting apparatus operate either at a constant forward inclination angle or they permit the measurement of the forward inclination angle for a natural head posture and body posture.
The vertical and horizontal centering data of the spectacles (XR, XL, YR, YL) need to be measured during the optical spectacle lens centering. From the Zeiss brochure 20-759-e it is known to do this with a video device in front of which the test person assumes a position at a distance of approximately 5 m. The centering data are then determined based on the video images. With this procedure, a correspondingly large space must be made available.
The optimal correction has as a condition precedent that the seating of the frame (anatomical fitting of spectacles) is taken into account in the fitting of the spectacles. The device “Video Infral” of Carl Zeiss AG detects the seating of the frame in three dimensions so that the previously determined correction values can be realized in the optimal spectacle lens. These correction values include, for example, spectacle lens diameter, weight of the spectacle lens, minimal peripheral thickness, minimal center thickness. Front and lateral recordings are made simultaneously by two video cameras and are digitalized and stored in the connected computer. In the digital images, the following can be marked: the position of the pupils, the position of the corneal vertex distance and the position of the characteristic contours of the frame. From these marks, the computer determines the optimal parameters of a spectacle lens for correct viewing by a spectacles wearer. The term “corneal vertex distance” is generally understood to be the distance between the image end vertex point of the spectacle lens and the cornea.
A video advisory system is disclosed in U.S. Pat. Nos. 4,922,338 and 4,991,005 and has a recording unit which records electronic images and is driven by a computer. A video advisory system of this kind serves to provide customer advice in optometry shops with the selection of a new spectacles frame.
Furthermore, a video device “Visu-Point” of Ulev GmbH is known wherein a test person fixates on an object at only a short distance (for example, at only 1 meter). This fixing object can, for example, be an LED mounted above a video camera. The video camera takes images of the test person while the test person views the fixing object. It is disadvantageous here that the convergence position of the pair of eyes is approximated via the purely geometric convergence. The convergence of the pair of eyes arises with the fixation.
U.S. Pat. No. 5,129,400 discloses an arrangement for investigating the tissue of the ocular fundus. A laser beam is used and a speckle is intended to be generated by the ocular fundus.